1. Field of the Invention
The present invention relates to a stable semi-insulating gallium arsenide single crystal which has a high resistivity in the dark and before being processed and is capable of keeping the high resistivity even under illumination or even after being processed, for example, subjected to annealing treatment or epitaxial growth.
2. Description of the Prior Art
The use of such a semi-insulating gallium arsenide single crystal has lately been enlarged as substrates for various planar type elements, for example, microwave elements such as shottky gate field effect transistors (MESFET) and Gunn diodes, optical semiconductor elements of optical integrated circuits, Hall elements, etc. It is industrially an important problem how the electrical property and crystalline quality of the above described substrates are realized with good reproducibility and, when the above described elements are produced by the epitaxial growth or ion-implantation method, there are many problems, for example, abnormal phenomena occurring at the interface between the semi-insulating gallium arsenide substrate and active layer during the production process, resistance-lowering phenomena of the substrate, etc., resulting in a large obstacle to increasing of the yield of these elements. Furthermore, in view of that the above described elements are often used under some illumination, it is a further problem whether the resistivity thereof is stable for light or not.